My mother was in a rehibilitation center for about 3 months after a bad fall. We had all her mail forwarded to my sister's house (different town, different county even). The mail carrier put a red tag in her mail box with a note "abandoned". I checked her box occasionally over that 3 months, and never was anything left. Everything got sent to my sisters.
We've had mail stopped at home when we've been gone (camping) for extended periods. Never had a problem with that.
When we moved from one house to another a few years ago, to a different county, we had all our mail forwarded to our new address. Because the old house did not sell immediately, we had to keep taking care of it. We often got mail at the old house.
I went to the post office and asked why mail was being delivered there. This was now, almost a year after we moved. They told me at the post office that any mail without our name on it was put in the box. Ours was being forwarded. They were correct. Looking back, everything in the box had someone elses name on it. (The address was definitely that house, but those people never lived there. It finally dawned on us that someone must have been using that address with bogus names (either stolen credit or someone purchasing items on credit and giving a bogus address as their residence. We found out, people actually do this. The use address for houses that are for sale. It's quite a racket actually.
We finally went back to the post office and told them we wanted ALL mail stopped at tha address. Filled out the form again, and that stopped that! We left specific instructions that the new owner (when it finally sold), had to go to the post office to get mail activated at that address or they'd probably never get it. Don't know what happened, but we never heard from the new owner.
Don't know if this helps anything or not, but maybe you could just put a "hold" on all your mail and have your son pick it up from the Post Office occasionally. I did this for my mother when she visited my other sister in Texas a few years ago. She was in Texas for about 5 months, about 5 years in a row. Post office was more than accommodating. This worked. Something to think about.